Oral contraceptive use and kidney cancer risk among women: evidence from a meta-analysis.

Previous studies have investigated the relationship between oral contraceptives (OCs) use and kidney cancer risk. However, they yielded inconsistent results. To our knowledge, a comprehensive assessment of the association between OC and kidney cancer risk has not been reported. Hence, we conducted a meta-analysis to quantify the association. We identified all relevant studies up to July 2014 through a literature search of using PubMed and EMBASE, and by reviewing the references from the retrieved articles. Fixed-effect and random-effect models were used to estimate summary relative risks (SRRs) and the corresponding 95% confidence intervals (CIs). A total of 12 studies were eligible and included in this meta-analysis, involving 4,206 kidney cancer cases and 638,677 participants. The SRR of kidney cancer for ever versus never OC use was 0.89 (95% CI: 0.82-0.98). The protection became stronger when compared the longest duration of OC use with never use (RR = 0.80; 95% CI: 0.68-0.94). In dose-response analysis, we found that the kidney cancer risk decreased by 2% for per 1 year increment in OC use (RR = 0.98; 95% CI: 0.96-0.99). No apparent heterogeneity was observed across studies included in this analysis. Egger's and Begg's test also indicated no publication bias. The present study suggested that OC may reduce the risk of kidney cancer, especially for long-term users. More well-conducted and large-scale prospective studies are warranted to confirm the effects of OC use on kidney cancer.